Actually, SetEventDamage truly modifies the damage dealt. For example, unrestricted damage at 100 reduced to 75 by reductions. With SetEventDamage to 200, damage dealt will become 200. That's because the damage event triggers before damage is actually dealt.
It's like the calculations are done beforehand, and you get to override them with SetEventDamage, so no fix.
The same with GetEventDamage. Unresisted flag makes it so that the function returns the damage value before any resistance was applied.
I know what SetEventDamage does. That was my request after all.